This Application claims the benefit of the priority of Japanese Application 11-046194, filed Feb. 24, 1999.
The present Invention is directed to a circuit board assembly, particularly designed for use in an electrical connection box located in the engine compartment of an automotive vehicle. More specifically, the Invention is intended to reliably secure the busbar to the insulative substrate upon which it is located.
A typical prior art assembly of the general type to which the present Invention is directed is shown in FIGS. 5(a) and 5(b). Circuit board assembly 50 includes insulative substrate 51 with busbar 53 mounted thereon. Upstanding ribs 52 are located at the edges of the substrate and surround at least a portion of the busbar.
At predetermined locations between upstanding ribs 52, bosses 56 project from insulative substrate 51. The bosses are substantially in the form of circular columns with heights which are greater than those of the upstanding ribs. At the base of boss 56 is taper 57, having a taper diameter L2, which reinforces the boss.
Busbar 53, which is stamped from a single sheet of metal, is disposed between upstanding ribs 52. Insertion opening 55 is provided in the busbar to permit the insertion of boss 56 therethrough. Once busbar 53 is in position, boss 56 is pressed downward, as shown in FIG. 5(b), to fix the busbar on the substrate, thereby completing circuit board assembly 50.
However, the foregoing assembly has certain defects. Since taper 57 extends upwardly from the upper surface of insulative substrate 51, insertion opening diameter L3 has to be greater than taper diameter L2 in order to permit this section to pass therethrough. In addition, busbar 53 must provide a predetermined width W on either side of insertion opening 55 in the radial direction thereof. Thus, the outer dimension of busbar 53 is equal to L3+2 W. The distance between busbar 53 and boss diameter L1 is wasted space which, upon exertion of pressure on boss 56, is filled by the expansion of the boss as shown in FIG. 5(b). Since busbar 53 must be of a predetermined minimum size in order to carry the amount of current required, the overall dimension is increased, requiring a larger insulative substrate than would otherwise be necessary. In addition to the size, the costs of production of the assembly, as well as those of the electrical connection box in which it will be housed, are also increased.
It is an object of the present Invention to overcome the foregoing problems and, in particular, provide a circuit board wherein wasted space is minimized or eliminated. As a result, the circuit boardxe2x80x94as well as the electrical connection box encasing itxe2x80x94is reduced in size, thereby cutting its cost.
The circuit board assembly according to the present Invention comprises an insulative substrate with a busbar disposed on the upper surface thereof. At least one cavity is provided in the insulative substrate and a boss projects therefrom. An expanded section of the boss is located adjacent the bottom of the cavity and the boss extends through the insertion opening in the cavity. By having the expanded section of the boss within the cavity, it is then possible to have the insertion opening in the busbar of smaller diameter than in the corresponding prior art opening. Thereafter, the boss is pressed toward the substrate to cause it to flatten out and overlie the busbar. At the same time, a slight expansion of the diameter of the boss takes place so that any gap between the periphery of the insertion hole and the boss is filled and the busbar is securely affixed to the insulative substrate.
The upper end of the expanded section may extend so that it is coplanar with the upper surface of the insulative substrate;
however, it is preferable that the expanded section be entirely within the substrate so that the upper end of the expanded section is below the plane of the upper surface of the insulative substrate. It is also preferable that the expanded section constitute a taper in the direction away from the bottom of the cavity. However, the Invention is not limited to a particular shape of the expanded section, it can be a shelf or in some other form, so long as it fits within the cavity and does not extend beyond it.
It has been found desirable to taper the distal end of the boss in the direction away from the substrate. This assists in inserting the boss into the insertion opening (or in placing the insertion opening over the boss).
Between the tapered portion of the boss and the expanded section, the central section, having a central diameter, is located. As a result, the insertion opening in the busbar can be made substantially the same diameter asxe2x80x94or only very slightly greater thanxe2x80x94the central diameter. This minimizes or eliminates any wasted space. If a small gap is present, it is readily filled when the boss is deformed under pressure, with or without the application of heat.
It has been found useful to provide a plurality of upstanding ribs on the upper surface of the insulative substrate. These add strength to the assembly and also serve to contain the busbar. It has also been found desirable to allow a slight gap between the perimeter of the busbar and the upstanding ribs adjacent thereto. This gap should preferably be equal to the gap (if any) between the busbar and the central section of the boss. It is also preferable that the boss be of sufficient height so that it extends above the ribs. This facilitates the application of pressure to the boss and its resultant flattening out to affix the busbar to the insulative substrate.
In production, the busbar is placed between the ribs on the upper surface of the insulated substrate with the boss extending through the insertion opening. Thereafter, pressure (and optionally heat) is exerted on the boss in the direction of the expanded section. This flattens the boss so that it overlies a portion of the substrate and also causes the central portion of the boss to expand and fill the central gap between the circumference of the insertion opening and the boss, thereby reliably securing the busbar to the substrate and completing the assembly.